CN107406100B - Work vehicle and method for controlling work vehicle - Google Patents

Abstract

The invention provides a work vehicle and a control method of the work vehicle. A wheel loader (1) is an articulated wheel loader (1) in which a front frame (11) and a rear frame (12) are connected, and is provided with: the vehicle control device comprises a joystick (24), an acting force applying part (27), a vehicle speed sensor (105) and a control part (28). The control lever (24) changes the steering angle (theta s) of the front frame (11) relative to the rear frame (12) by the operation of an operator. The urging force applying unit (27) applies an assisting urging force or a reaction force to the operation of the joystick (24) by the operator. A vehicle speed sensor (105) detects the speed of the wheel loader (1). A control unit (28) controls an acting force application unit (27) to apply an assist force or a reaction force in accordance with the speed detected by a vehicle speed sensor (105).

Description

Work vehicle and method for controlling work vehicle

Technical Field

The present invention relates to a work vehicle and a method of controlling the work vehicle.

Background

As an articulated work vehicle, a configuration has been disclosed in which a steering angle is changed by controlling a flow rate of oil supplied to a hydraulic actuator disposed astride a front frame and a rear frame (see, for example, patent documents 1 and 2).

In the work vehicle disclosed in patent documents 1 and 2, the pilot pressure is changed by changing the open/close state of the pilot valve port by operating the joystick by the operator. The steering angle of the work vehicle is changed by adjusting the flow rate of the hydraulic actuator supplied from the steering valve in accordance with the changed pilot pressure.

Since the steering angle is changed by the hydraulic pressure, the operator can change the steering angle by applying only a light operation force to the joystick, the operation force being necessary to change the open/close state of the pilot valve port.

Documents of the prior art

Patent document

Patent document 1: japanese unexamined patent publication No. 11-105723

Patent document 2: japanese unexamined patent publication No. 11-321664

Disclosure of Invention

However, in the work vehicles of patent documents 1 and 2, since the operational feeling of the operator is determined by the operational force required to change the open/close state of the pilot valve port, even when the speed of the work vehicle is changed, the operational feeling of the operator's operation member is the same, and it is difficult to achieve both improvement of the operability during low-speed traveling and stability of the linear travel during high-speed traveling.

That is, when the operation feeling is set to be easy with importance given to improvement of the operability during low-speed running, the stability of the linear travel during high-speed running is deteriorated, and when the operation feeling is set to be heavy with importance given to the stability of the linear travel during high-speed running, the operability during low-speed running is deteriorated.

In view of the problems of the conventional work vehicle described above, an object of the present invention is to provide a work vehicle and a method of controlling a work vehicle that can improve operability during low-speed travel and stability of straight line travel during high-speed travel.

(means for solving the problems)

A work vehicle according to a first aspect of the present invention is an articulated work vehicle in which a front frame and a rear frame are coupled to each other, the articulated work vehicle including: the joystick includes a joystick, an acting force applying unit, a speed detecting unit, and a control unit. The joystick is operated by an operator to change the steering angle of the front frame with respect to the rear frame. The urging force applying unit applies an assist urging force or a reaction force to the operation of the joystick by the operator. The speed detection unit detects a speed of the work vehicle. The control unit controls the acting force applying unit to apply the assisting force or the reaction force according to the speed detected by the speed detecting unit.

In this way, since the assist force or the reaction force can be applied to the operation of the joystick in accordance with the speed of the work vehicle, the operation force required for the operation of the joystick can be changed.

Therefore, the operating force required for operating the joystick is set to be small during low-speed running and to be large during high-speed running, so that the operability during low-speed running and the stability of straight traveling during high-speed running can be improved.

In the work vehicle according to the second aspect of the invention, the control unit controls the biasing force applying unit such that the higher the speed detected by the speed detecting unit, the greater the operating force required to operate the joystick.

Thus, the higher the speed can be made in a stepwise or continuous manner, the greater the operating force required for operating the joystick.

Therefore, since the operational feeling of the joystick becomes strong at a high speed and the operational feeling of the joystick becomes relaxed at a low speed, the operability during low-speed traveling and the stability of linear traveling during high-speed traveling can be improved.

A work vehicle according to a third aspect of the present invention is the work vehicle according to the second aspect of the present invention, wherein the control unit controls the biasing force applying unit to apply the reaction force when the speed detected by the speed detecting unit is equal to or higher than a predetermined speed set in advance, and to apply the assist force when the speed detected by the speed detecting unit is lower than the predetermined speed.

When the work vehicle is driven at a high speed, the operational feeling can be enhanced by applying a reaction force when the joystick is operated, and the running stability at a high speed can be improved.

A work vehicle according to a fourth aspect of the present invention is the work vehicle according to the second aspect of the present invention, wherein the control unit controls the biasing force application unit such that the assist biasing force applied to the joystick decreases as the speed detected by the speed detection unit increases.

This makes it possible to increase the operating force required for operating the joystick as the speed increases, for example, in a stepwise or continuous manner, thereby improving the operability during low-speed travel and the stability of linear travel during high-speed travel.

A work vehicle according to a fifth aspect of the present invention is the work vehicle according to the first aspect of the present invention, further including a torque detection unit. The control unit controls the biasing force applying unit based on the torque detected by the torque detecting unit to apply the assist biasing force or the reaction force to the operation of the joystick.

This allows the operator to apply a biasing force in accordance with the torque applied to the joystick. For example, the magnitude of the applied biasing force can be controlled so as to increase the assist biasing force applied by the biasing force applying portion when the torque applied to the joystick by the operator is large and to decrease the assist biasing force when the torque is small.

A work vehicle according to a sixth aspect of the present invention is the work vehicle according to the first aspect of the present invention, and includes a hydraulic actuator and a control valve. The hydraulic actuator changes the steering angle. The control valve is connected to the joystick and controls the flow rate of oil supplied to the hydraulic actuator. The control valve has: a first input member, a second input member, and a biasing portion. The first input member is coupled to the joystick and is displaced according to an operation amount of the joystick. The second input member is displaced according to the steering angle. The urging portion urges the first input member to be located at a neutral position where a displacement amount of the first input member coincides with a displacement amount of the second input member. The control unit controls the flow rate of oil supplied to the hydraulic actuator based on a difference between the displacement amount of the first input member and the displacement amount of the second input member. The operating lever is operated against the urging force of the urging portion.

Thus, when the steering angle is changed following the joystick after the joystick is operated, the control valve is set to the neutral position when the operation amount of the joystick is matched with the steering angle.

In this way, the control valve is provided with the biasing portion, and the operator operates the joystick with the operation force against the biasing force of the biasing portion. An assist force or a reaction force can be applied to the operation against the applied force.

The work vehicle according to a seventh aspect of the present invention is the work vehicle according to the sixth aspect of the present invention, further comprising a steering valve. The steering valve adjusts the flow rate of oil supplied to the hydraulic actuator based on the pilot pressure input from the control valve. The control valve controls the flow rate of oil supplied from the steering valve to the hydraulic actuator by adjusting the pilot pressure.

Thus, the pilot pressure is adjusted by the operation of the operator, and the supply amount of oil flowing from the steering valve to the hydraulic actuator is controlled, thereby changing the steering angle of the front frame with respect to the rear frame.

The work vehicle according to an eighth aspect of the present invention is the work vehicle according to the seventh aspect, further including: a hydraulic actuator, a control valve, and a coupling portion. The hydraulic actuator changes the steering angle. The control valve is connected to the joystick and controls the flow rate of oil supplied to the hydraulic actuator. The connecting part connects the operating lever and the control valve. The force applying section has a motor and a transmission mechanism. The motor generates an assist or reaction force. The transmission mechanism transmits the assist force or the reaction force of the motor to the connection portion.

This allows the biasing force of the motor to be transmitted to the connection portion that connects the joystick and the control valve, and the operating force required for operating the joystick can be changed.

A ninth aspect of the present invention is a method for controlling an articulated work vehicle in which a front frame and a rear frame are coupled to each other, the method including: a speed detection step, and an application step. The speed detecting step detects a speed of the work vehicle. The applying step applies an assist force or a reaction force to the operation of the joystick by the operator, which changes the steering angle of the front frame with respect to the rear frame, based on the detected speed.

In this way, the assist force or the reaction force can be applied to the operation of the joystick in accordance with the speed of the work vehicle, and therefore the operation force required for the operation of the joystick can be changed.

Therefore, the operating force required for operating the joystick is set to be small during low-speed running and to be large during high-speed running, so that the operability during low-speed running and the stability of straight traveling during high-speed running can be improved.

(Effect of the invention)

According to the present invention, it is possible to provide a work vehicle and a method of controlling a work vehicle, which can improve operability during low-speed travel and stability of straight line travel during high-speed travel.

Drawings

Fig. 1 is a side view of a wheel loader according to an embodiment of the present invention.

Fig. 2 is a hydraulic circuit diagram showing a configuration of a steering operation device of the wheel loader of fig. 1.

Fig. 3 is a sectional view showing the structure of the pilot valve of fig. 2.

Fig. 4(a) and (b) are cross-sectional views in the direction of the arrow between AA 'of fig. 3, and fig. 4(c) and (d) are cross-sectional views in the direction of the arrow between BB' of fig. 3.

Fig. 5 is a side view showing the connection portion and the link mechanism of fig. 2.

Fig. 6 is a view of the joystick of fig. 5 as viewed from above.

Fig. 7(a) is a schematic view of the pilot valve of fig. 3, (b) is a view showing a relationship between a body-rod deviation angle and a rod reaction force of the pilot valve of fig. 7(a), (c) is an arrow-direction cross-sectional view between CC ', DD', EE 'and FF' of fig. 7(a) when the deviation angle α is 0, (d) is an arrow-direction cross-sectional view between CC ', DD', EE 'and FF' of fig. 7(a) when the deviation angle α is θ 2, and (e) is an arrow-direction cross-sectional view between CC ', DD', EE 'and FF' of fig. 7(a) when the deviation angle α is θ 3.

Fig. 8 is a perspective view showing the structure of the urging force applying portion of fig. 2.

Fig. 9(a) is a diagram showing assist forces with respect to the lever input torque at three different vehicle speeds in the present embodiment, and (b) is a diagram showing a lever reaction force with respect to a vehicle body-lever deviation angle between the case where the assist force shown in fig. 9(a) is applied and the case where the assist force is not applied.

Fig. 10 is a flowchart showing a wheel loader control method according to a first embodiment of the present invention.

Fig. 11 is a diagram showing assist forces with respect to the lever input torque at three different vehicle speeds in a modification of the present embodiment.

Fig. 12 is a configuration diagram showing a steering operation device according to a modification of the embodiment of the present invention.

Fig. 13 is a structural diagram showing a biasing force applying unit according to a modification of the embodiment of the present invention.

Detailed Description

A wheel loader according to an embodiment of the present invention will be described below with reference to the drawings.

(first embodiment)

< 1. Structure >

(1-1. overview of wheel loader configuration)

Fig. 1 is a schematic diagram showing a structure of a wheel loader 1 according to the present embodiment. The wheel loader 1 of the present embodiment includes: a vehicle body frame 2, a working device 3, a pair of front tires 4, a cab 5, an engine compartment 6, a pair of rear tires 7, and a steering operation device 8 (see fig. 2 described later).

The wheel loader 1 performs a sand loading operation and the like using the working device 3.

The vehicle body frame 2 is of a so-called articulated type, and includes: a front frame 11, a rear frame 12, and a connecting shaft portion 13. The front frame 11 is disposed forward of the rear frame 12. The connecting shaft 13 is provided at the center in the vehicle width direction, and connects the front frame 11 and the rear frame 12 to be swingable with each other. The pair of front tires 4 are attached to the left and right of the front frame 11. The pair of rear tires 7 are attached to the right and left sides of the rear frame 12.

The working device 3 is driven by working oil from a working device pump, not shown. The working device 3 includes: boom 14, bucket 15, lift cylinder 16, and bucket cylinder 17. The large arm 14 is mounted to the front frame 11. A bucket 15 is mounted to the front end of the boom 14.

The lift cylinder 16 and the bucket cylinder 17 are hydraulic cylinders. One end of the lift cylinder 16 is attached to the front frame 11, and the other end of the lift cylinder 16 is attached to the boom 14. The boom 14 swings up and down by the extension and contraction of the lift cylinder 16. One end of the bucket cylinder 17 is attached to the front frame 11, and the other end of the bucket cylinder 17 is attached to the bucket 15 via a bell crank 18. The bucket cylinder 17 extends and contracts, and the bucket 15 swings up and down.

The cab 5 is mounted on the rear frame 12, and includes a steering wheel and a joystick 24 (see fig. 2 described later) for steering operation, an operation lever for operating the working device 3, various display devices, and the like. The engine compartment 6 is located on the rear side of the cab 5, is disposed on the rear frame 12, and houses an engine.

The steering operation device 8 includes steering cylinders 21 and 22, and changes the traveling direction of the wheel loader 1 by changing the steering angle of the front frame 11 with respect to the rear frame 12 by changing the flow rate of the oil supplied to the steering cylinders 21 and 22, as will be described later in detail.

(1-2. steering device)

Fig. 2 is a hydraulic circuit diagram showing the configuration of the steering operation device 8. The steering operation device 8 of the present embodiment mainly includes: a pair of steering cylinders 21, 22, a steering hydraulic circuit 23, a joystick 24, a link 25, a link mechanism 26, an urging force applying portion 27, and a control portion 28.

(1-2-1. steering cylinder)

The pair of steering cylinders 21 and 22 are hydraulically driven. The pair of steering cylinders 21, 22 are arranged in parallel on the left and right sides in the vehicle width direction with the connecting shaft portion 13 interposed therebetween. The steering cylinder 21 is disposed on the left side of the connecting shaft portion 13 (see fig. 1). The steering cylinder 22 is disposed on the right side of the connecting shaft portion 13. The steering cylinders 21 and 22 have one end attached to the front frame 11 and the other end attached to the rear frame 12.

The steering cylinder 21 is provided with an extension port 21a and a contraction port 21b, and the steering cylinder 22 is provided with an extension port 22a and a contraction port 22 b.

When oil is supplied to the extension port 21a of the steering cylinder 21 and the contraction port 22b of the steering cylinder 22 and oil is discharged from the contraction port 21b of the steering cylinder 21 and the extension port 22a of the steering cylinder 22, the steering cylinder 21 extends and the steering cylinder 22 contracts. This changes the steering angle θ s, and the vehicle turns to the right. When oil is supplied to the contraction port 21b of the steering cylinder 21 and the extension port 22a of the steering cylinder 22 and oil is discharged from the extension port 21a of the steering cylinder 21 and the contraction port 22b of the steering cylinder 22, the steering cylinder 21 contracts and the steering cylinder 22 extends. This changes the steering angle θ s, and the vehicle turns left.

A steering angle detection unit 104 that detects the steering angle θ s is provided in the vicinity of the connecting shaft 13 disposed between the steering cylinders 21 and 22. The steering angle detection unit 104 is constituted by, for example, a potentiometer, and transmits the detected steering angle θ s to the control unit 28 as a detection signal.

The steering cylinder 21 is provided with a cylinder stroke sensor 106 for detecting a cylinder stroke, and the steering cylinder 22 is provided with a cylinder stroke sensor 107 for detecting a cylinder stroke. The detection values of the cylinder stroke sensors 106 and 107 may be transmitted to the control unit 28 to detect the steering angle θ s.

(1-2-2. steering hydraulic circuit)

The steering hydraulic circuit 23 is a hydraulic circuit for adjusting the flow rate of oil supplied to the steering cylinders 21 and 22. The steering hydraulic circuit 23 includes a main hydraulic circuit 30 and a pilot hydraulic circuit 40.

(a) Main hydraulic circuit

The main hydraulic circuit 30 is a circuit for supplying oil from a main hydraulic source 31 to the steering cylinders 21 and 22, and includes a steering valve 32. The main hydraulic source 31 is constituted by a hydraulic pump, a relief valve, and the like.

The steering valve 32 is a flow rate adjustment valve that adjusts the flow rate of oil supplied to the steering cylinders 21 and 22 in accordance with the input pilot pressure. The steering valve 32 has: a main oil inlet P1, a main oil discharge port P2, a first diverting port P3, and a second diverting port P4. The main oil inlet P1 is connected to the main hydraulic source 31 via the main hydraulic line 36. The main oil discharge port P2 is connected to the recovered oil discharge groove DT via the main oil discharge line 37. The first steering port P3 is connected to the contraction port 21b of the steering cylinder 21 and the extension port 22a of the steering cylinder 22 via the first steering line 38. The second steering port P4 is connected to the extension port 21a of the steering cylinder 21 and the contraction port 22b of the steering cylinder 22 via a second steering line 39.

The steering valve 32 has a valve body 33 movable in a neutral position Ns, a left steering position Ls, and a right steering position Rs. When the valve body 33 is disposed at the neutral position Ns, the main inlet port P1 communicates with the main outlet port P2. In this case, the first steering port P3 and the second steering port P4 do not communicate with either port. When the valve body 33 is disposed at the left steering position Ls, the main oil inlet P1 communicates with the first steering port P3, and the main oil discharge port P2 communicates with the second steering port P4. When the valve body 33 is disposed at the right steering position Rs, the main oil inlet P1 communicates with the second steering port P4, and the main oil discharge port P2 communicates with the first steering port P3.

The steering valve 32 has a first pilot chamber 34 and a second pilot chamber 35. When the pilot pressure is not supplied to the first pilot chamber 34 and the second pilot chamber 35, and when the same pilot pressure is supplied to the first pilot chamber 34 and the second pilot chamber 35, the valve body 33 is located at the neutral position Ns. In a state where only the pilot pressure is supplied to the first pilot chamber 34, the valve body 33 is located at the left steering position Ls. In a state where only the pilot pressure is supplied to the second pilot chamber 35, the valve body 33 is located at the right steering position Rs. When the valve body 33 is located at the left steering position Ls and the right steering position Rs, the steering valve 32 changes the opening area through which the oil from the main hydraulic pressure source 31 passes, in accordance with the supplied pilot pressure. Thus, the steering valve 32 controls the flow rate of the oil supplied to the steering cylinder 21 or 22 in accordance with the pilot pressure.

(b) Pilot hydraulic circuit

The pilot hydraulic circuit 40 is a circuit for supplying oil from the pilot hydraulic source 43 to the first pilot chamber 34 and the second pilot chamber 35 of the steering valve 32.

The pilot hydraulic circuit 40 includes a variable decompression portion 41 and a pilot valve 42.

(i) Variable decompression portion

The variable decompression section 41 decompresses and adjusts the hydraulic pressure supplied from the pilot hydraulic pressure source 43 to the pilot valve 42. The variable relief portion 41 incorporates an electromagnetic relief valve, and receives a command signal from the control portion 28 to control the hydraulic pressure.

(ii) Pilot valve

The pilot valve 42 is a rotary valve that adjusts a pilot pressure input from the pilot hydraulic pressure source 43 to the steering valve 32.

(structural overview of Pilot valve)

The rotary pilot valve 42 has: a pilot pump port P5, a pilot drain port P6, a first pilot port P7, and a second pilot port P8. The pilot pump port P5 is connected to the variable relief portion 41 via the pilot hydraulic line 44, and the variable relief portion 41 is connected to the pilot hydraulic source 43. The pilot oil drain port P6 is connected to the drain groove DT for the recovered oil via the pilot oil drain line 45. The first pilot port P7 is connected to the first pilot chamber 34 of the steering valve 32 via the first pilot conduit 46. The second pilot port P8 is connected to the second pilot chamber 35 of the steering valve 32 via a second pilot conduit 47.

The pilot valve 42 has a valve body 60 including an operation spool 71 and an operation sleeve 72, and the operation spool 71 is movable in a neutral position Np, a left pilot position Lp, and a right pilot position Rp with reference to the operation sleeve 72.

When the operation spool 71 is located at the neutral position Np with respect to the operation sleeve 72, the pilot pump port P5, the pilot drain port P6, the first pilot port P7, and the second pilot port P8 communicate with each other. When the operation spool 71 is disposed at the left pilot position Lp with respect to the operation sleeve 72, the pilot pump port P5 communicates with the first pilot port P7, and the pilot drain port P6 communicates with the second pilot port P8. When the operation spool 71 is disposed at the right pilot position Rp with respect to the operation sleeve 72, the pilot pump port P5 communicates with the second pilot port P8, and the pilot drain port P6 communicates with the first pilot port P7.

Fig. 3 is a structural sectional view of the pilot valve 42.

The pilot valve 42 mainly has: a valve body portion 60, an operation input shaft 61, a feedback input shaft 62, a housing 63, a first spring 64, a second spring 65, and a feedback portion 66.

(operation input shaft)

The operation input shaft 61 is rotatably provided around the center axis O thereof and is inserted into the housing 63. The operation input shaft 61 is coupled to a joystick 24 described later via a coupling portion 25. The operation input shaft 61 is rotated at the same rotation angle as the rotation angle θ in of the joystick 24 to the left and right.

(feedback input shaft)

The feedback input shaft 62 is disposed on the same shaft as the operation input shaft 61 and is rotatably provided around the center axis O. The feedback input shaft 62 is inserted into the housing 63 so as to face the operation input shaft 61. The feedback input shaft 62 is connected to the front frame 11 via a link mechanism 26 described later, and rotates at the same rotational angle as the steering angle θ s of the front frame 11 with respect to the rear frame 12.

(case)

The housing 63 has a substantially cylindrical space, and the operation input shaft 61 and the feedback input shaft 62 are inserted therein as described above. The housing 63 houses the valve body portion 60 and the feedback portion 66, and is formed with a pilot pump port P5, a pilot drain port P6, a first pilot port P7, and a second pilot port P8.

(valve body part)

The valve body portion 60 includes an operation spool 71 and an operation sleeve 72, and the operation spool 71 is rotated with respect to the operation sleeve 72 to be located at a neutral position Np, a left pilot position Lp, and a right pilot position Rp.

The operation valve body 71 is substantially cylindrical, is disposed on the same shaft as the operation input shaft 61, and is connected to the operation input shaft 61. The joystick 24 is connected to the operation input shaft 61 via a coupling portion 25 described later, and when the operator operates the joystick 24 to the right side by a rotation angle θ in, the operation input shaft 61 and the operation valve body 71 also rotate to the right about the central axis O by the rotation angle θ in. Further, notches 71a and 71b are formed in the circumferential direction at two positions facing each other with the center axis O interposed therebetween on the operation input shaft 61 side of the operation valve body 71.

The operation sleeve 72 is substantially cylindrical, is located outside the operation valve body 71, and is rotatably disposed inside the housing 63 with respect to the operation valve body 71 and the housing 63.

In the present specification, the right rotation and the left rotation indicate rotation directions when viewed from above.

(first spring)

The first spring 64 is inserted between the mutually rotatable operation spool 71 and the operation sleeve 72, and generates a reaction force corresponding to a difference in mutual rotation angle.

Fig. 4(a) is a cross-sectional view taken along the arrow between AA' perpendicular to the central axis O. As shown in fig. 4(a), the operation valve body 71 is provided with rectangular holes 71c and 71d in diametrically opposed walls, respectively. Rectangular grooves 72c and 72d are formed in diametrically opposed walls at one end of the operation sleeve 72 on the operation input shaft 61 side. The first spring 64 is formed of two sets of plate spring portions 64a in which a plurality of convex plate springs are overlapped. The two sets of plate spring portions 64a are arranged so that the convex portions face each other so as to form an X shape in fig. 4 (a). The two sets of plate spring portions 64a penetrate through the holes 71c, 71d of the operation valve body 71, and both ends penetrate into the grooves 72c, 72d of the operation sleeve 72. In this way, the operation spool 71 and the operation sleeve 72 are coupled by the first spring 64.

As shown in fig. 4(a), the state in which the position of the hole 71c substantially coincides with the position of the groove 72c in the circumferential direction and the position of the hole 71d substantially coincides with the position of the groove 72d in the circumferential direction is the state in which the valve body portion 60 is located at the neutral position Np.

Then, by operating the joystick 24, as shown in fig. 4(b), the operation spool 71 rotates relative to the operation sleeve 72, and the operation spool 71 moves relative to the operation sleeve 72 toward the left pilot position Lp or the right pilot position Rp. When the joystick 24 is rotationally operated to the right, the operation spool 71 rotates to the right with respect to the operation sleeve 72, and moves to the right pilot position Rp. When the joystick 24 is rotated to the left, the operation spool 71 rotates to the left with respect to the operation sleeve 72, and the left pilot position Lp moves.

When this movement is performed, the operator moves the operating lever 24 against the elastic force of the first spring 64, and therefore a lever reaction force is generated in the operating lever 24. In other words, the first spring 64 biases the operation spool 71 to be located at the neutral position Np with respect to the operation sleeve 72.

(feedback section)

On the other hand, the feedback unit 66 feeds back the steering angle θ s of the front frame 11 with respect to the rear frame 12 to the valve body unit 60. The feedback unit 66 mainly includes: a feedback spool 73, a feedback sleeve 74, a drive shaft 75, a first center pin 76, and a restriction 78.

The propeller shaft 75 is positioned between the operation input shaft 61 and the feedback input shaft 62, and is disposed on the same axis (central axis O) as the operation input shaft 61 and the feedback input shaft 62. The transmission shaft 75 is disposed inside the operation valve body 71. A first center pin 76 is disposed at one end of the transmission shaft 75 on the operation input shaft 61 side, perpendicular to the center axis O. Both ends of the first center pin 76 are fixed to the operating sleeve 72 through the cutouts 71a, 71 b. As will be described in detail later, the first center pin 76 and the notches 71a and 71b restrict the rotational angle of the operation valve body 71 with respect to the operation sleeve 72 to an angle within a predetermined range. Further, since the first center pin 76 is fixed to the operation sleeve 72 and the transmission shaft 75, when the transmission shaft 75 rotates, the operation sleeve 72 integrated with the transmission shaft 75 also rotates.

The feedback valve body 73 is substantially cylindrical, is disposed on the same axis as the feedback input shaft 62, and is connected to the feedback input shaft 62. Notches 73a and 73b are formed in the feedback valve body 73 on the feedback input shaft 62 side in the circumferential direction at two positions facing each other with the center axis O therebetween. A transmission shaft 75 is disposed inside the feedback valve body 73. The feedback input shaft 62 is connected to the front frame 11 via a link mechanism 26 described later, and when the front frame 11 rotates to the right with respect to the rear frame 12 by a steering angle θ s, the feedback input shaft 62 and the feedback valve 73 also rotate to the right by a rotation angle θ s equal to the steering angle θ s.

The feedback sleeve 74 is substantially cylindrical, is located outside the feedback spool 73, and is rotatably disposed inside the housing 63 with respect to the feedback spool 73 and the housing 63.

The restriction portion 78 restricts the rotation of the feedback sleeve 74 with respect to the feedback spool 73 to an angle within a predetermined range. The restricting portion 78 is constituted by the second center pin 77 and wall portions 73ae and 73be (see fig. 7 described later) at both ends of the cutouts 73a and 73b in the circumferential direction.

The second center pin 77 is disposed at one end of the transmission shaft 75 on the feedback input shaft 62 side, perpendicular to the center axis O. Both ends of the second center pin 77 are fixed to the feedback sleeve 74 through the cutouts 73a, 73 b. The rotation of the feedback sleeve 74 with respect to the feedback spool 73 is restricted to an angle within a predetermined range by the second center pin 77 and the notches 73a and 73 b. Further, since the second center pin 77 is fixed to the feedback sleeve 74 and the transmission shaft 75, when the feedback sleeve 74 rotates, the transmission shaft 75 integrated with the feedback sleeve 74 also rotates. By the rotation of the transmission shaft 75, the operation sleeve 72 fixed to the transmission shaft 75 by the first center pin 76 is rotated.

(second spring)

The second spring 65 is inserted between the feedback spool 73 and the feedback sleeve 74, which are rotatable relative to each other, and generates a reaction force corresponding to a rotational difference relative to each other. Fig. 4(c) is a cross-sectional view in the direction of the arrow between BB' of fig. 3.

As shown in fig. 4(c), the feedback spool 73 has rectangular holes 73c and 73d in diametrically opposite walls.

Rectangular grooves 74c and 74d are formed in diametrically opposed walls at one end of the feedback sleeve 74 on the feedback input shaft 62 side, respectively. The second spring 65 is formed of two sets of plate spring portions 65a in which a plurality of convex plate springs are stacked. The two sets of plate spring portions 65a are arranged so that the convex portions face each other so as to form an X shape in fig. 4 (c). The two sets of plate spring portions 65a penetrate through the holes 73c, 73d of the feedback spool 73, and both ends penetrate into the grooves 74c, 74d of the feedback sleeve 74. Thus, the feedback spool 73 and the feedback sleeve 74 are coupled by the second spring 65. In the state of fig. 4(c), the hole 73c and the groove 74c are circumferentially aligned, and the hole 73d and the groove 74d are circumferentially aligned. In this way, the feedback sleeve 74 is biased by the second spring 65 so that the positions of the grooves 74c and 74d in the circumferential direction match the positions of the holes 73c and 73d of the feedback valve body 73 in the circumferential direction.

The first spring 64 is bent until the operation spool 71 is restricted with respect to the operation sleeve 72, but the second spring 65 is set so as to start bending by applying a biasing force equal to or greater than a reaction force generated until the first spring 64 is restricted.

As will be described in detail later with reference to fig. 7, when the operation spool 71 is rotated to a limited angle with respect to the operation sleeve 72 and the lever 24 is operated, the second spring 65 is bent and the feedback sleeve 74 is rotated with respect to the feedback spool 73 as shown in fig. 4 (d). Fig. 4(d) is a cross-sectional view in the direction of the arrow between BB' of fig. 3, and the arrow in the rotational direction is reversed compared to fig. 4(b) because it is viewed from below.

That is, when the lever 24 is operated at an angle or more at which the operation spool 71 is restricted with respect to the operation sleeve 72, the operator needs to operate the lever 24 against the urging force of the second spring 65.

With the above-described configuration of the feedback portion 66, when the feedback input shaft 62 rotates in accordance with a change in the steering angle, the feedback spool 73 rotates, and the feedback sleeve 74 coupled to the feedback spool 73 via the second spring 65 also rotates. Then, the operation sleeve 72 fixed to the feedback sleeve 74 via the second center pin 77, the transmission shaft 75, and the first center pin 76 rotates, and the difference between the rotation angles of the operation spool 71 and the operation sleeve 72 changes, whereby the pilot pressure is changed.

That is, in the pilot valve 42, the position of the operation spool 71 relative to the operation sleeve 72 is moved to the neutral position Np, the left pilot position Lp or the right pilot position Rp in accordance with the difference α between the rotation angle θ in of the operation input shaft 61 and the rotation angle fb of the feedback input shaft 62 (which coincides with the steering angle θ s). when the rotation angle difference α is 0, the operation spool 71 is located at the neutral position Np. relative to the operation sleeve 72, and when the operation spool 71 is located at the left pilot position Lp or the right pilot position Rp relative to the operation sleeve 72, the pilot valve 42 changes the opening area through which the oil from the pilot hydraulic pressure source 43 passes in accordance with the rotation angle difference α. thus, the pilot pressure fed from the pilot valve 42 to the steering valve 32 is adjusted in accordance with the rotation angle difference α.

The operation input shaft 61 is provided with a first rotation angle detection unit 101 formed of, for example, a rotation sensor. The first rotation angle detection section 101 detects a rotation angle θ in of the operation input shaft 61. The feedback input shaft 62 is provided with a second rotation angle detection unit 102 formed of a rotation sensor, for example. The second rotation angle detection unit 102 detects a rotation angle θ fb (═ θ s) of the feedback input shaft 62. The rotation angles θ in and θ fb detected by the first rotation angle detection unit 101 and the second rotation angle detection unit 102 are transmitted to the control unit 28 as detection signals.

As described above, the steering angle detection unit 104 detects the steering angle θ s also on the connecting shaft portion 13, but the steering angle detection unit 104 may not be provided because the rotation angle θ fb of the feedback input shaft 62 matches the steering angle θ s.

(1-2-3. Joystick, connecting part)

Fig. 5 is a side view showing the structure inside the cab 5. A driver seat 5a on which an operator sits is provided in the cab 5. A steering box 80 is disposed on the left side of the driver seat 5a in the vehicle width direction.

The joystick 24 is disposed to protrude forward and obliquely upward from the steering box 80.

The connecting portion 25 connects the lever 24 and the pilot valve 42. The coupling portion 25 mainly has: a steering shaft 81, a connecting rod 82, and a universal joint portion 83.

The steering shaft 81 is disposed in the vertical direction, and is rotatably supported by the steering box 80 about the center axis E thereof. The connecting rod 82 is disposed in the steering box 80 and connects the steering lever 24 and the steering shaft 81.

Specifically, the steering shaft 81 is configured by connecting a rod-side shaft 81a, an input shaft 81b, and a valve-side shaft 81c in this order (see fig. 8 described later). That is, one end of the rod-side shaft 81a is connected to the connecting rod 82, and the other end of the rod-side shaft 81a is connected to one end of the input shaft 81 b. The other end of the input shaft 81b is connected to one end of the valve-side shaft 81c, and the other end of the valve-side shaft 81c is connected to the universal joint 83. The input shaft 81b receives an assist force or a reaction force from a force applying portion 27 described later.

The universal joint portion 83 couples the steering operation shaft 81 to the operation input shaft 61 of the pilot valve 42 disposed near the driver seat 5 a. The gimbal portion 83 has a central portion 83a that is extendable and retractable, and joint portions 83b and 83c disposed at both ends of the central portion 83 a. The joint 83b is coupled to the steering shaft 81. The joint 83c is coupled to the operation input shaft 61.

Fig. 6 is a plan view of the vicinity of the joystick 24 as viewed from above. As shown in fig. 6, the joystick 24 is formed to protrude obliquely upward from an arc-shaped hole 84 formed in the upper surface of the steering box 80. The joystick 24 is rotatable in the horizontal direction about a steering operation shaft 81 (specifically, a central axis E). Further, an R-sign is formed at the right end edge of the hole 84 of the turn box 80, and an L-sign is formed at the left end edge.

For example, as shown in fig. 6, when the operator rotates the joystick 24 from the center position to the right side by the rotation angle θ in, the steering operation shaft 81 is also rotated to the right by the rotation angle θ in. The rotation of the rotation angle θ in of the steering operation shaft 81 is transmitted to the operation input shaft 61 via the universal joint portion 83, and the operation input shaft 61 is also rotated rightward by the rotation angle θ in. The same is true when the joystick 24 is rotated leftward.

(1-2-4. Link mechanism)

The link mechanism 26 has: a follower rod 91, a follower link 92, and a bracket 93.

The follower link 92 is fixed to the feedback input shaft 62 of the pilot valve 42. The bracket 93 is fixed to the front frame 11. The follower link 92 connects the follower lever 91 to the bracket 93.

The pilot valve 42 disposed in the rear frame 12 is connected to the front frame 11 by the link mechanism 26.

The steering angle θ s of the front frame 11 with respect to the rear frame 12 is set to the same angle as the rotation angle θ fb of the feedback input shaft 62 by the link mechanism 26.

That is, when the front frame 11 is rotated to the right side about the coupling shaft portion 13 with respect to the rear frame 12 by the steering angle θ s, the feedback input shaft 62 is also rotated to the right by the rotation angle θ s via the link mechanism 26, and when the steering angle θ s is rotated to the left, the feedback input shaft 62 is also rotated to the left by the rotation angle θ s via the link mechanism 26.

(1-2-5. bar reaction force)

Next, the lever reaction forces generated by the first spring 64 and the second spring 65 when the operating lever 24 is operated will be described.

Fig. 7(a) is a diagram schematically showing the pilot valve 42, fig. 7(b) is a diagram showing the relationship between the body-lever deviation angle and the lever reaction force, it should be noted that the body-lever deviation angle α is the difference (θ in- θ fb) between the rotation angle θ in of the steering lever 24 and the steering angle θ s (θ fb) of the front frame 11 with respect to the rear frame 12, fig. 7(c) is an arrow-direction sectional view between CC ', DD', EE 'and FF' of fig. 7(a) when the deviation angle α is 0, fig. 7(d) is an arrow-direction sectional view between CC ', DD', EE 'and FF' of fig. 7(a) when the deviation angle α is θ 2, fig. 7(e) is an arrow-direction sectional view between CC ', DD', EE 'and FF' of fig. 7(a) when the deviation angle α is θ 3, fig. 7(b) is a diagram showing the directions between CC ', DD', EE 'and FF' and fig. 7(b) is a diagram illustrating the control lever deviation angle, which is not described above, and which is considered for convenience.

When the operator rotates the joystick 24 from the center position by the rotation angle θ in, the operation input shaft 61 is also rotated by the rotation angle θ in. On the other hand, since the response of the steering cylinders 21 and 22 is delayed, the steering angle θ s gradually increases following the rotation angle θ in. The rotation angle θ in of the joystick 24 indicates a target steering angle, and the steering angle θ s indicates an actual steering angle. The feedback input shaft 62 also rotates at the same rotation angle θ s as the steering angle θ s in accordance with the change in the steering angle θ s. Then, the feedback spool 73 also rotates together with the feedback input shaft 62, and by this rotation, the feedback sleeve 74 coupled via the second spring 65 also rotates.

Here, since the feedback sleeve 74 and the operation sleeve 72 are integrated by the first center pin 76, the second center pin 77, and the transmission shaft 75, the operation sleeve 72 also rotates due to the rotation of the feedback sleeve 74.

That is, the difference between the rotational angle of the operation valve body 71 and the rotational angle of the operation sleeve 72 corresponds to the deviation angle α (see fig. 4 (b)).

Since the first spring 64 biases the operation valve body 71 to the neutral position Np with respect to the operation sleeve 72, the lever 24 needs to be operated against the biasing force of the first spring 64 in order to increase the offset angle α.

The first spring 64 has a spring characteristic S1 shown in fig. 7(b) in the spring characteristic S1 of the first spring 64, in order to rotate the operation input shaft 61, an urging force equal to or greater than the initial reaction force F1 (the urging force required to start bending the first spring 64) is required to operate the operating lever 24, and in the spring characteristic S1 of the first spring 64, the lever reaction force increases as the deviation angle α increases, that is, the urging force required for the operation of the operating lever 24 also increases as the deviation angle α increases.

As shown in fig. 7(c), in the neutral position Np where the deviation angle α is 0, the first center pin 76 is disposed at the center of the notches 71a and 71b of the operation spool 71, and the second center pin 77 is disposed at the center of the notches 73a and 73b of the feedback spool 73.

When the lever 24 is rotated to the right side, for example, to increase the offset angle α, and the offset angle α reaches the angle θ 2, as shown in fig. 7(d), the first center pin 76 abuts against the wall portion 71ae formed in the circumferential direction of the notch 71a and the wall portion 71be formed in the circumferential direction of the notch 71b, and at this time, the second center pin 77 is disposed at the center of the notches 73a and 73b of the feedback spool 73 because the initial reaction force (the force required to start bending the second spring 65) is set to F2. as shown in the spring characteristic S2 of the second spring 65 when the reaction force generated by the first spring 64 when the offset angle α is the angle θ 2 is F2, and the initial reaction force of the second spring 65 may be set to be larger than F2 as long as F2 or more.

Further, in order for the operator to rotate the operating lever 24 to the right, the operator needs to operate against the reaction force of the second spring 65. That is, when the lever 24 is further rotated to the right, the first center pin 76 abuts against the wall portion 71be and the wall portion 71ae, and therefore, when the operation valve body 71 is rotated, it is necessary to rotate together with the operation sleeve 72. As described above, the operation sleeve 72 and the feedback sleeve 74 are integrated, and the feedback spool 73 is connected to the feedback input shaft 62. Therefore, when the operating lever 24 is further operated to rotate rightward, it is necessary to operate against the reaction force of the second spring 65 as shown in fig. 7 (d).

When the deviation angle α reaches θ 3, as shown in fig. 7(e), the second center pin 77 abuts against the wall portion 73ae formed in the circumferential direction of the notch 73a and the wall portion 73be formed in the circumferential direction of the notch 73b, and thus the second center pin 77 can rotate by the angle (θ 3- θ 2), that is, the pilot valve 42 is configured such that the deviation angle α is not larger than the angle θ 3, and therefore, as shown in fig. 7(b), the lever reaction force linearly increases at the angle θ 3, and when the abutment of the second center pin 77 against the wall portions 73ae and 73be strong, a sharp reaction occurs, which puts a burden on the wrist of the operator, and the angle θ 3 is also referred to as a catch angle (キャッチアップ).

In fig. 7 b, although the case where the joystick 24 is rotationally operated to the right is described as an example, the case where the joystick 24 is rotationally operated to the left is also the same, and in this case, the deviation angle α is a negative value (see the two-dot chain line L7 in fig. 9 b described later), that is, when the deviation angle α reaches- θ 2, the first center pin 76 abuts against the wall portions 71ae and 71be, and the second center pin 77 abuts against the wall portions 73ae and 73be at an angle of- θ 3. in this way, the pilot valve 42 is configured such that the absolute value of the deviation angle α is not larger than the angle θ 3.

Note that, although the rotation angle of the operation valve member 71 and the rotation angle of the operation sleeve 72 are different until the deviation angle α reaches θ 2, the opening degree of the pilot valve 42 is constant because there is no difference in the rotation angle between the operation valve member 71 and the operation sleeve 72 when the deviation angle α exceeds the angle θ 2, and the opening degree of the pilot valve 42 is constant even when the deviation angle α is between the angles θ 2 to θ 3, but the variable decompression portion 41 may be controlled to change the pilot pressure in accordance with the deviation angle.

(1-2-6. force applying part)

Fig. 8 is a perspective view showing the urging force applying portion 27.

The urging force applying portion 27 applies an assist urging force or a reaction force to the operation of the lever 24. The urging force applying section 27 includes an electric motor 111 and a worm gear section 112. The worm gear part 112 has a cylindrical worm 112a and a worm wheel 112 b. The worm wheel 112b is provided around the input shaft 81b and meshes with the cylindrical worm 112 a. An output shaft of the electric motor 111 is connected to the cylindrical worm 112a, so that the cylindrical worm 112a rotates about its central axis. The electric motor 111 is driven based on a command from a drive circuit 204 provided in the control unit 28.

The first end 81b1 of the input shaft 81b is connected to the rod-side shaft 81a, and the second end 81b2 is connected to the valve-side shaft 81 c.

When the electric motor 111 is driven, the cylindrical worm 112a rotates, and the worm wheel 112b rotates due to the rotation, so that a rotational force is also generated in the input shaft 81b fixed to the worm wheel 112 b. By changing the rotation direction of the cylindrical worm 112a, a rotational force can be applied to the input shaft 81b in either of the left-hand rotation direction and the right-hand rotation direction.

For example, when the joystick 24 is rotated rightward, the assist force is applied to the operation of the joystick 24 by applying a force in the rightward rotation direction to the input shaft 81 b. When the joystick 24 is rotated rightward, a reaction force is applied to the operation of the joystick 24 by applying a force to the input shaft 81b in the leftward rotation direction.

The input shaft 81b is provided with a torque sensor 103. The torque sensor 103 detects a torque generated in the input shaft 81b by the operator applying a biasing force to the joystick 24. The torque sensor 103 of the present embodiment detects the rotation direction of the input shaft 81b and the torque generated in the input shaft 81b by detecting the torsion of the torsion bar with a coil, for example. The detected rotation direction and torque T are output to the control unit 28 as a steering torque signal.

(1-2-7. control section)

The control unit 28 includes an arithmetic device such as a CPU and a storage device such as a RAM and a ROM.

The control unit 28 outputs command signals to the motor 111 and the variable decompression unit 41 by wire or wireless, thereby controlling the motor 111 and the variable decompression unit 41.

The rotation angle θ in of the operation input shaft 61 detected by the first rotation angle detection unit 101, the rotation angle θ fb (═ θ s) of the feedback input shaft 62 detected by the second rotation angle detection unit 102, and the steering angle θ s detected by the steering angle detection unit 104 are input to the control unit 28 as detection signals.

The vehicle speed V detected by the vehicle speed sensor 105 shown in fig. 2 is also input to the control unit 28 as a detection signal. The torque T detected by the torque sensor 103 is also input to the control unit 28 as a steering torque signal.

The control unit 28 controls the variable decompression unit 41 based on the rotation angle θ in, the rotation angle θ fb (═ θ s), and the vehicle speed V. Thus, the original pressure of the pilot pressure supplied to the pilot valve 42 can be controlled so that the flow rate of the oil flowing to the left and right steering cylinders 21, 22 is not sharply reduced.

The control unit 28 controls the motor 111 based on the rotation angle θ in, the rotation angle θ fb (═ θ s), the vehicle speed V, and the steering torque signal (including the torque T).

In this way, the control unit 28 can drive the motor 111 based on the value of the torque T and apply an assist force or a reaction force to the operation of the joystick 24 by the operator.

< 2. action >

Next, the steering operation of the wheel loader 1 according to the present embodiment will be described.

(2-1. steering operation)

When the joystick 24 is located at the center position, the operation input shaft 61 is located at a predetermined initial position, and the rotation angle θ in of the operation input shaft 61 is 0. Further, since the steering angle θ s is also 0, the feedback input shaft 62 is also located at a predetermined initial position. In the present embodiment, the steering angle θ s represents an angle from a state along the front-rear direction with respect to the rear frame 12 when the state is 0, as shown in fig. 7 (a). As shown in fig. 6, the rotation angle θ in represents a rotation angle from the center position of the joystick 24. In the calculation of the deviation angle, for example, the rotation to the right may be calculated as a positive angle and the rotation to the left may be calculated as a negative angle.

At this time, the operation valve body 71 is located at a neutral position Np shown in fig. 4(a) with respect to the operation sleeve 72. In this case, the pilot pressures in the first pilot chamber 34 and the second pilot chamber 35 of the steering valve 32 are the same, and the valve body 33 of the steering valve 32 is also at the neutral position Ns. Therefore, the supply or discharge of oil to the left and right steering cylinders 21 and 22 is not performed, the steering angle θ s is maintained at 0, and the rotation angle θ fb (θ s) of the feedback input shaft 62 is also maintained at 0.

Next, when the operator applies the operation force Fin to rotate the joystick 24 rightward from the center position as shown in fig. 6, the operation input shaft 61 rotates rightward in the same manner as the joystick 24 when the operation force Fin exceeds F1 of the first spring 64, and the rotation angle θ in of the operation input shaft 61 increases, and at this time, the reaction of the left and right steering cylinders 21 and 22 is delayed, so the steering angle θ s remains in a state of 0, and the rotation angle θ fb (θ s) of the feedback input shaft 62 is also 0, and therefore, the deviation angle (α — θ s) between the rotation angle θ in and the steering angle θ s increases.

The operation spool 71 rotates rightward with respect to the operation sleeve 72 together with the rotation of the operation input shaft 61. Here, the operation sleeve 72 and the feedback sleeve 74 are integrated, and the feedback sleeve 74 is coupled to the feedback spool 73 by the second spring 65. Then, the initial reaction force F2 of the second spring 65 is equal to or greater than the reaction force of the spring characteristic S1 of the first spring 64 shown in fig. 7 (b). Therefore, the operating sleeve 72 is connected to the operating spool 71 so as not to rotate, and the operating spool 71 rotates rightward with respect to the operating sleeve 72.

As a result, the operation spool 71 rotates rightward relative to the operation sleeve 72, and moves to the right pilot position Rp, thereby supplying the pilot pressure to the second pilot port P8 and the pilot pressure to the second pilot chamber 35.

Thereby, the valve body 33 of the steering valve 32 moves to the right steering position Rs, and oil is supplied to the extension port 21a of the steering cylinder 21 and the contraction port 22b of the steering cylinder 22, and oil is discharged from the contraction port 21b of the steering cylinder 21 and the extension port 22a of the steering cylinder 22. As a result, the steering angle θ s gradually increases, and the front frame 11 faces the right direction (see R in fig. 2) with respect to the rear frame 12. This change in the steering angle θ s is transmitted to the feedback input shaft 62 via the link mechanism 26, and the feedback input shaft 62 rotates at a rotation angle θ s.

When the operator stops the joystick 24 at the predetermined rotation angle θ 1, the operation input shaft 61 is also stopped at the rotation angle θ 1, on the other hand, the steering angle θ s is gradually increased, so the rotation angle θ s of the feedback input shaft 62 is also increased, the feedback spool 73 is also rotated together with the feedback input shaft 62, and the feedback sleeve 74 coupled to the feedback spool 73 via the second spring 65 is also rotated, the feedback sleeve 74 is integrated with the operation sleeve 72 via the first center pin 76, the second center pin 77, and the transmission shaft 75, so the operation sleeve 72 is also rotated together with the rotation of the feedback sleeve 74, the difference (deviation angle α) between the rotation angles of the operation sleeve 72 and the operation spool 71 is reduced due to the rotation of the operation sleeve 72, then, when the steering angle θ s (θ s of the feedback input shaft 62) reaches θ 1 (the rotation angle θ in of the operation input shaft 61), the deviation angle α is 0, at this time, the operation spool 71 of the pilot valve 42 is positioned at the neutral position Np. with respect to the operation sleeve 72, the first steering valve 34 and the pilot chamber 34 is also kept at the rotation angle 3621, and the pilot chamber 35 is not supplied with the pilot oil or the pilot oil to the steering cylinder 22.

When the joystick 24 is rotated to the right side and stopped at the predetermined rotation angle θ 1 in this way, the steering angle θ s is also maintained at the same rotation angle θ 1. Thereby, the front frame 11 is maintained at the rotation angle θ 1 to the right side with respect to the rear frame 12.

When the operator returns the joystick 24 from the right position to the center position, the operation input shaft 61 is also rotated, and the rotation angle θ in of the operation input shaft 61 decreases, and at this time, the steering angle θ s remains at the rotation angle θ 1 because the reaction of the left and right steering cylinders 21 and 22 is delayed, and therefore, the difference α (θ in — θ s) between the rotation angles decreases from 0 to a negative value, and the operation spool 71 rotates leftward with respect to the operation sleeve 72, moves to the left pilot position Lp, and supplies pilot pressure to the first pilot port P7, whereby the valve body 33 of the steering valve 32 moves to the left steering position, supplies oil to the contraction port 21b of the steering cylinder 21 and the extension port 21a of the steering cylinder 22, and discharges oil from the extension port 21a of the steering cylinder 21 and the expansion port 21b of the steering cylinder 22, and the steering angle θ s gradually decreases from the rotation angle θ 1, and the change in the rotation angle θ s is transmitted to the feedback input shaft 62 through the link mechanism 26, and the feedback input shaft 62 is rotated by the same change in the rotation angle θ s.

When the operator stops the joystick 24 at the center position, the operation input shaft 61 is also stopped at the initial position, that is, the position where the rotation angle θ in is 0, on the other hand, the steering angle θ s is also gradually decreased from the rotation angle θ 1, so the difference between the rotation angles (deviation angle) α is gradually decreased, and then, when the steering angle θ s is 0, the rotation angle θ fb (θ s) of the feedback input shaft 62 is also 0, and the difference between the rotation angles α is 0, in this case, the operation spool 71 is disposed at the neutral position Np. with respect to the operation sleeve 72, and therefore, the pilot pressures of the first pilot chamber 34 and the second pilot chamber 35 of the steering valve 32 are the same, and the steering valve 32 is also at the neutral position Ns., and therefore, the supply or discharge of oil to the left and right steering cylinders 21, 22 is not performed, and the steering angle θ s is also returned and maintained at 0, whereby the front frame 11 is returned to the rear frame 12 in the front-rear direction.

Note that, when the joystick 24 is rotated to the left, the same description as above is omitted.

(2-2. control of force applying part)

Next, the control of the biasing force applying unit 27 when the joystick 24 is operated will be described.

The wheel loader 1 of the present embodiment controls the biasing force applying unit 27 so as to change the biasing force applied to the operation of the joystick 24 in accordance with the vehicle speed. More specifically, the control unit 28 of the wheel loader 1 controls the acting force applying unit 27 such that the higher the speed detected by the vehicle speed sensor 105, the greater the operating force required to operate the joystick 24.

The control unit 28 stores assist force information indicating an assist force to be applied to the torque input by the joystick 24 at each vehicle speed, and controls the force application unit 27 based on the assist force information.

(2-2-1. auxiliary force information)

Fig. 9(a) is a diagram showing assist force (assist force information) applied to the input torque at each vehicle speed. Fig. 9(a) shows the assist force (assist force information) applied to the lever input torque in the case where the vehicle speed is 0km/h (solid line L1), in the case where the vehicle speed is 25km/h (broken line L2), and in the case where the vehicle speed is 40km/h (one-dot chain line L3).

In the assist force information shown in fig. 9(a), in the case where the vehicle speed is 0km/h (L1) and the case where the vehicle speed is 25km/h (L2), the assist force applied to the lever input torque is a positive value, and the assist force is applied to the operation of the joystick 24. That is, when the joystick 24 is rotated to the right, the biasing force applying portion 27 is controlled to apply a biasing force to the input shaft portion 81b in the rightward rotational direction. Further, when the joystick 24 is rotated leftward, the biasing force applying portion 27 is controlled to apply a biasing force to the input shaft portion 81b in the leftward rotation direction.

When the vehicle speed was 0km/h (L1) and the vehicle speed was 25km/h (L2), the assistance force applied to the lever input torque was greater in the case of 0km/h than in the case of 25 km/h.

As shown in fig. 9(a), when the vehicle speed is 40km/h (L3), the assist force applied to the lever input torque is negative, and a reaction force is applied to the operation of the joystick 24.

That is, when the lever 24 is rotated to the right, the biasing force applying portion 27 applies a biasing force to the input shaft portion 81b in the left rotational direction, and when the lever 24 is rotated to the left, the biasing force applying portion 27 applies a biasing force to the input shaft portion 81b in the right rotational direction. This requires a large operation force when operating the joystick 24.

Since the steering torque signal input from the torque sensor 103 includes not only the magnitude of the torque but also the information on the rotation direction, the control unit 28 recognizes the operation direction of the joystick 24 based on the information on the rotation direction, and rotates the motor 111 in an appropriate direction at each speed.

Fig. 9(b) is a diagram showing the lever reaction force with respect to the deviation angle α in the case where the assist force information shown in fig. 9(a) is applied and in the case where the assist force information is not applied, the solid line L4 shows the lever reaction force with respect to the vehicle body-lever deviation angle in the case where the vehicle speed is 0km/h, the broken line L5 shows the lever reaction force with respect to the vehicle body-lever deviation angle in the case where the vehicle speed is 25km/h, the one-dot chain line L6 shows the lever reaction force with respect to the vehicle body-lever deviation angle in the case where the vehicle speed is 40km/h, the two-dot chain line L7 shows the lever reaction force with respect to the vehicle body-lever deviation angle in the case where the assist force is not applied, and shows the same state as the lever reaction force of fig. 7(b), in fig. 9(b), the positive deviation angle α shows the case where the joystick 24 is moved to the right side, and the negative deviation angle α shows the case where the joystick 24 is moved to.

As shown in fig. 9(b), since the reaction force is applied to the operation of the joystick 24 by the force application unit 27 when the vehicle speed is 40km/h, the lever reaction force in the case (L6) where the vehicle speed is 40km/h is larger than that in the case (L7) where no force is applied.

Further, in the case where the vehicle speed is 25km/h (L5) and the case where the vehicle speed is 0km/h (L4), the assist force is applied to the joystick 24 by the force application unit 27, so that the lever reaction force is smaller in the case where the vehicle speed is 25km/h (L5) and the case where the vehicle speed is 0km/h (L4) than in the case where no force is applied (L7).

As described above, when the assist force information of fig. 9(a) is used to apply the force to the operation of the joystick 24, the lever reaction force is small in a state where the vehicle speed is slow, and the lever reaction force is increased when the vehicle speed is fast.

Accordingly, the lever reaction force is small at low speed, so that the joystick 24 is easily operated, and operability is improved, and the lever reaction force is large at high speed, so that the joystick 24 is hardly operated, and traveling stability is improved.

As described above, the assist force information set for each speed shown in fig. 9(a) is stored in the control portion 28. The control unit 28 may store the assist force information as a curve or a straight line, or may store the assist force information as a table (a table of assist forces set for each lever input torque at predetermined intervals).

(2-2-2. control action)

Fig. 10 is a flowchart showing the control operation of the urging force applying unit 27.

When the joystick 24 is operated, the control unit 28 acquires a steering torque signal from the torque sensor 103 in step S110. The steering torque signal is a signal including information on the direction of rotation and the magnitude of torque generated by the rotation thereof.

Next, in step S120, control unit 28 determines the steering direction of joystick 24 based on the steering torque signal. The rotation direction of the motor 111 when the biasing force is applied is determined based on the steering direction.

Next, in step S130, the control unit 28 acquires a detection value from the vehicle speed sensor 105.

Next, in step S140, the control unit 28 determines the assist force based on the stored assist force information (see fig. 9 (a)).

The control unit 28 stores the three pieces of assist torque information (when the vehicle speed is 0km/h, 25km/h, 40km/h) shown in fig. 9 (a). When the detection value from the vehicle speed sensor 105 is between three speeds (for example, 12km/h), the control unit 28 calculates the assist torque at the vehicle speed by interpolation calculation. In this way, the assist torque is calculated by interpolation calculation, and thus the assist torque can be continuously changed in accordance with the speed change.

Next, in step S150, the control unit 28 outputs a command torque signal to the drive circuit 204 based on the determined assist force and the rotation direction of the input shaft 81b (which may be the rotation direction of the joystick 24), drives the motor 111, and applies a force to the operation of the joystick 24 via the connection unit 25.

< 3. characteristics, etc. >

(1)

As shown in fig. 2, a wheel loader 1 (an example of a work vehicle) according to the present embodiment is an articulated wheel loader 1 that connects a front frame 11 and a rear frame 12, and includes: a joystick 24, an urging force applying section 27, a vehicle speed sensor 105 (an example of a speed detecting section), and a control section 28. The steering lever 24 is operated by an operator to change a steering angle θ s of the front frame 11 with respect to the rear frame 12. The urging force applying unit 27 applies an assist urging force or a reaction force to the operation of the joystick 24 by the operator. The vehicle speed sensor 105 detects the speed of the work vehicle. The control section controls the acting force applying section 27 to apply the assisting force or the reaction force according to the speed detected by the vehicle speed sensor 105.

In this way, since the assist force or the reaction force can be applied to the operation of the joystick 24 in accordance with the speed of the wheel loader 1, the operation force required for the operation of the joystick 24 can be changed.

Therefore, by setting the operation force required for operating the joystick 24 during low-speed running to be small and setting the operation force required for operating the joystick 24 during high-speed running to be large, the operability during low-speed running and the stability of straight traveling during high-speed running can be improved.

In addition, the wheel loader 1 travels by tires as compared with a crawler type work vehicle, and therefore the vehicle speed is high. Therefore, it is more preferable for the work vehicle such as the wheel loader 1 to travel by tires to achieve both operability during low-speed travel and stability of linear travel during high-speed travel.

(2)

In the wheel loader 1 (an example of a work vehicle) according to the present embodiment, the control unit 28 controls the biasing force applying unit 27 such that the higher the speed detected by the vehicle speed sensor 105, the greater the operating force required to operate the joystick 24.

As a result, as shown in fig. 9(b), the higher the speed can be made in a gradient manner, the larger the operation force required for operating the joystick 24.

Therefore, since the operational feeling of the joystick 24 is increased at high speed and the operational feeling of the joystick 24 is relaxed at low speed, the operability during low speed running and the stability of the straight traveling during high speed running can be improved.

(3)

In the wheel loader 1 (an example of a work vehicle) according to the present embodiment, as shown in fig. 9(a), the control unit 28 controls the biasing force applying unit so that the reaction force is applied when the speed detected by the vehicle speed sensor 105 is equal to or higher than a predetermined speed set in advance, and so that the assist force is applied when the speed detected by the vehicle speed sensor 105 is lower than the predetermined speed.

When the wheel loader 1 is driven at a high speed, the operational feeling can be enhanced by applying a reaction force when the joystick 24 is operated, and the running stability at a high speed can be improved.

As the predetermined speed, for example, a high speed threshold may be set to 25km per hour, and the control unit 28 determines that the speed is high when the speed detected by the vehicle speed sensor 105 is 25km or more, and applies a reaction force to the operation of the joystick 24 as shown in fig. 9 (a). On the other hand, when the speed detected by the vehicle speed sensor 105 is less than 25km per hour, the control unit 28 determines that the speed is medium or low, and applies the assist force to the operation of the joystick 24.

The speed is not limited to 25km per hour, and as shown by curves L2 and L3 in fig. 9(a), a speed between 25km per hour and 40km per hour may be set as a predetermined speed.

(4)

The wheel loader 1 (an example of a work vehicle) according to the present embodiment further includes a torque sensor 103 (an example of a torque detection unit) as shown in fig. 8. The control unit 28 controls the biasing force applying unit 27 based on the torque detected by the torque sensor 103 to apply an assist biasing force or a reaction force to the operation of the joystick 24.

This allows the lever 24 to be biased in response to the torque applied by the operator. For example, the magnitude of the applied biasing force can be controlled so as to increase the assist biasing force applied by the biasing force applying portion 27 when the torque applied to the joystick 24 by the operator is large and to decrease the assist biasing force when the torque is small.

(5)

As shown in fig. 2, the wheel loader 1 (an example of a working vehicle) according to the present embodiment includes steering cylinders 21 and 22 (an example of a hydraulic actuator) and a pilot valve 42 (an example of a control valve), the steering cylinders 21 and 22 change a steering angle θ s, the pilot valve 42 is connected to a joystick 24 to control a flow rate of oil supplied to the steering cylinders 21 and 22, the pilot valve 42 includes an operation input shaft 61 (an example of a first input member), a feedback input shaft 62 (an example of a second input member), a first spring 64 (an example of an urging portion), and a second spring 65 (an example of an urging portion), the operation input shaft 61 (an example of a first input member) is connected to the joystick 24 and is displaced according to a rotation angle (an example of an operation amount) of the joystick 24, the feedback input shaft 62 is displaced according to a steering angle θ s, the first spring 64 and the second spring 65 urge the operation input shaft 61 so that a rotation angle θ in (an example of a rotation angle θ s) of the operation input shaft 61 coincides with a θ s of the feedback input shaft 62, the first spring 64 and the second spring 65 urge the operation input shaft 61 so that the operation input shaft 21 and the return input shaft 21 and the control input shaft 21 and the return oil supply the control the flow rate of the control valve according to a difference between the rotation angle θ s of the operation input shaft 8522 and the operation input shaft 85s of the control input shaft.

Thus, when the steering lever 24 is operated, the steering angle θ s changes following the steering lever 24, and the rotation angle θ s of the steering lever 24 matches the steering angle θ s, the pilot valve 42 is in the neutral position Np.

In this way, the pilot valve 42 is provided with the first spring 64 and the second spring 65, and the operator operates the operating lever 24 with an operating force that opposes the urging forces of the first spring 64 and the second spring 65. An assist force or a reaction force can be applied to the operation against the applied force.

(6)

The wheel loader 1 (an example of a work vehicle) according to the present embodiment further includes a steering valve 32, as shown in fig. 2. The steering valve 32 adjusts the flow rate of oil supplied to the steering cylinders 21 and 22 (an example of a hydraulic actuator) based on a pilot pressure input from a pilot valve 42 (an example of a control valve). The pilot valve 42 controls the flow rate of the oil supplied from the steering valve 32 to the steering cylinders 21 and 22 by adjusting the pilot pressure.

Thus, the pilot pressure is adjusted by the operation of the operator, the supply amount of the oil flowing from the steering valve 32 to the steering cylinders 21 and 22 is controlled, and the steering angle θ s of the front frame 11 with respect to the rear frame 12 is changed.

(7)

As shown in fig. 2, the wheel loader 1 (an example of a work vehicle) according to the present embodiment further includes: the steering cylinders 21 and 22 (an example of a hydraulic actuator), the pilot valve 42 (an example of a control valve), and the connecting portion 25. The steering cylinders 21, 22 change the steering angle θ s. The pilot valve 42 is coupled to the joystick 24 and controls the flow rate of oil supplied to the steering cylinders 21 and 22. The connecting portion 25 connects the lever 24 and the pilot valve 42. The force applying unit 27 includes a motor 111 and a worm part 112 (an example of a transmission mechanism). The motor 111 generates an assist force or a reaction force. The worm part 112 transmits the assist force or the reaction force of the motor 111 to the coupling part 25.

This allows the biasing force of the motor 111 to be transmitted to the connecting portion 25 connecting the joystick 24 and the pilot valve 42, and the operating force required for operating the joystick 24 can be changed.

(8)

As shown in fig. 10, a method of controlling the wheel loader 1 (an example of a work vehicle) according to the present embodiment is a method of controlling the articulated wheel loader 1 in which the front frame 11 and the rear frame 12 are coupled, and includes: step S130 (an example of a speed detection step), and steps S140 and S150 (an example of an urging force application step). Step S130 (an example of the speed detection step) detects the speed of the wheel loader 1. Steps S140 and S150 (an example of the urging force applying step) apply the assist urging force or the reaction force to the operation of the joystick 24 by the operator who changes the steering angle θ S of the front frame 11 with respect to the rear frame 12, based on the detected speed.

In this way, since the assist force or the reaction force can be applied to the operation of the joystick 24 in accordance with the speed of the wheel loader 1, the operation force required for the operation of the joystick 24 can be changed.

Therefore, by setting the operation force required for operating the joystick 24 during low-speed running to be small and setting the operation force required for operating the joystick 24 during high-speed running to be large, the operability during low-speed running and the stability of straight traveling during high-speed running can be improved.

[ other embodiments ]

Although the above description has been made on one embodiment of the present disclosure, the present disclosure is not limited to the above embodiment, and various modifications can be made within a scope not departing from the gist of the present disclosure.

(A)

In the above embodiment, the reaction force is applied to the operation of the joystick 24 at a high speed (for example, when the vehicle speed is 40km/h), but the reaction force may not be applied, and the assist force smaller than that at a medium speed (for example, when the vehicle speed is 25 km/h) may be applied. In this case, the assist force per speed with respect to the lever input torque is represented in fig. 11. As shown in the assist force information of L3' (one-dot chain line) when the vehicle speed is 40km/h, the assist force (assist force) is set to gradually decrease from a low speed to a high speed.

This makes it possible to continuously increase the speed and the operating force required for operating the joystick, for example, and to improve the operability during low-speed travel and the stability of linear travel during high-speed travel.

(B)

In the above embodiment, the reaction force is applied to the operation of the joystick 24 only at the high speed, but the reaction force may be applied to the middle speed or both the middle speed and the low speed. In this case, the higher the speed, the larger the magnitude of the reaction force to be applied.

(C)

In the above embodiment, the control unit 28 stores the assist force information of three speeds (0km/h, 25km/h, 40km/h), but is not limited to the above speeds. The assist force information is not limited to three, and may be two or four or more. When the assist force is smoothly changed according to the speed, it is preferable to set the assist force to three or more.

(D)

In the above embodiment, the control unit 28 stores three pieces of assist force information, and continuously changes the assist force according to the speed by interpolation calculation, but may change the assist force in a gradient manner.

For example, the assist force information at the low speed is indicated by a solid line L1 in fig. 9(a), the assist torque information at the medium speed is indicated by a broken line L2 in fig. 9(a), and the assist force information at the high speed is indicated by a one-dot chain line L3 in fig. 9 (b). Then, for example, the low speed is set to a speed less than 15km/h, the medium speed is set to a speed of 15km/h or more and less than 25km/h, and the high speed is set to a speed of 25km/h or more and 40km/h or less. For example, 15km/h can be set as the first threshold value, and 25km/h can be set as the second threshold value.

In the above case, when the joystick 24 is operated, the control unit 28 compares the speed detected by the vehicle speed sensor 105 with the first threshold value and the second threshold value, and determines which of the low speed, the medium speed, and the high speed the vehicle speed corresponds to. Then, the assist force is determined from the steering torque signal using the assist force information of the determined speed. The speed is not limited to three steps, and may be divided into only two steps or may be further divided into three steps.

(E)

In the above-described embodiment, the operation direction of the joystick 24 is also detected by the torque sensor 103, but the detection of the operation direction may be performed based on a change in the rotation angle detected by the first rotation angle detection unit 101, or may be performed based on an angle difference (θ in- θ s) (also referred to as a deviation angle) between the rotation angle θ in detected by the first rotation angle detection unit 101 and the steering rotation angle θ fb (═ θ s) detected by the second rotation angle detection unit 102.

In this case, the detection values of the first rotation angle detection unit 101 and the second rotation angle detection unit 102 are input to the control unit 28, and the control unit 28 calculates the vehicle-to-lever deviation angle α. then, in step S120 shown in fig. 10, the steering direction of the joystick 24 is determined based on the vehicle-to-lever deviation angle α.

The vehicle-body-lever deviation angle α may be calculated from the steering angle θ s detected by the steering angle detection unit 104 and the rotation angle θ in detected by the first rotation angle detection unit 101, without using the detection value detected by the second rotation angle detection unit 102.

The vehicle-body-rod deviation angle α may be calculated from the steering angle θ s calculated from the detection values of the cylinder stroke sensors 106 and 107 and the rotation angle θ in detected by the first rotation angle detection unit 101.

(F)

In the above embodiment, the joystick 24 and the pilot valve 42 are mechanically coupled by the coupling portion 25, but the present invention is not limited thereto. Instead of mechanically coupling the joystick 24 and the pilot valve, the operation of the joystick 24 may be electrically transmitted to the pilot valve to operate the pilot valve.

Fig. 12 is a diagram showing a steering operation device 8 'as an example of a configuration for electrically transmitting the operation of the joystick 24 to the pilot valve 42'. The pilot valve 42' shown in fig. 12 is not of a rotary type as in the above embodiment, but of a spool type. The pilot valve 42 ' has a valve body portion 60 including a spool 71 ' and a sleeve (not shown), and is configured to be able to move the spool 71 ' to a neutral position Np, a left pilot position Lp, and a right pilot position Rp based on a signal from the control portion 28 with reference to the sleeve.

In the structure shown in fig. 12, for example, the gimbal portion 83 shown in fig. 5 is not provided. The joystick 24 is connected to a steering shaft 81. The steering shaft 81 is not coupled to the pilot valve. The urging force applying portion 27 applies the assist urging force or the reaction force to the steering operation shaft 81, as in the above-described embodiment. The first rotation angle detection unit 101 detects the rotation angle θ in of the steering shaft 81 and transmits the rotation angle θ in to the control unit 28.

In the steering operation device 8 ', the pilot valve 42' is of a spool type. The link mechanism 26 shown in fig. 5 that connects the pilot valve and the front frame 11 is not provided. The steering angle detecting unit 104 detects a steering angle θ s of the front frame 11 with respect to the rear frame 12, and sends the steering angle θ s to the control unit 28.

The control unit 28 sends a command to the pilot valve 42 ' based on the received information of the rotation angle θ in and the steering angle θ s, and controls the movement of the valve body 71 ' of the pilot valve 42 '. By the movement of the valve body 71 ', the pilot pressure supplied from the pilot valve 42' to the steering valve 32 changes, and the amount of oil supplied from the steering valve 32 to the steering cylinders 21 and 22 changes. Thereby performing the steering operation. At this time, the control unit 28 may perform control so as to reduce the difference between θ in and θ s by controlling the pilot pressure so that the rotation angle θ in matches the steering angle θ s.

In the steering operation device 8 ', the biasing force of the motor 111 is transmitted to the steering operation shaft 81 through the worm gear part 112, but the rotational shaft of the motor 111 may be directly connected to the steering operation shaft 81 without passing through a speed reduction device such as the worm gear part 112 as in the biasing force applying part 27' shown in fig. 13.

In the steering operation device 8 shown in fig. 5, the joystick 24 itself can be turned toward the inside or the outside of the driver's seat about the vertical axis. As shown in fig. 12, the operating lever 24 of the steering operation device 8 'may be rotatable toward the inside or the outside of the driver's seat about a horizontal axis. Therefore, the pilot valve 42' may be operated by the operation of the joystick 24, and the biasing force from the biasing force applying portion 27 may be transmitted to the joystick 24.

It should be noted that the electrical transmission may be performed by any means, wired or wireless.

(G)

In the above embodiment, the assist force is determined based on the value of the torque sensor, but the control may be performed so that the assist force is uniformly applied at each speed without providing a torque sensor. Specifically, the assist force may be applied at a constant value at each of the high speed, the medium speed, and the low speed, and the value of the assist force may be decreased in the order of the low speed, the medium speed, and the high speed, without depending on the torque generated by the operation of the joystick 24.

As described above, the determination as to which direction the joystick 24 is moved to the left or right can be made based on the change in the rotation angle of the first rotation angle detection unit 101.

(H)

In the above embodiment, the supply amount of the oil supplied from the steering valve 32 to the steering cylinders 21 and 22 is controlled based on the pilot pressure input from the pilot valve 42, which is an example of the control valve, but the oil from the pilot valve 42 may be directly supplied to the steering cylinders 21 and 22.

(I)

In the above embodiment, two springs, i.e., the first spring 64 and the second spring 65, are provided, but the second spring 65 may not be provided. In this case, for example, the feedback spool 73 and the feedback sleeve 74 may be fixed to each other.

(J)

In the above embodiment, the urging force is generated by the motor 111, but the present invention is not limited to the motor, and may be a hydraulic motor or the like.

(K)

In the above embodiment, the drive circuit 204 is included in the control unit 28, but only the drive circuit 204 may be mounted in a separate form without being included in the control unit 28. Further, the drive circuit 204 may be installed in the motor.

(L)

In the above embodiment, the wheel loader 1 has been described as an example of the working vehicle, but the present invention is not limited to the wheel loader, and may be an articulated dump truck, a motor grader, or the like as long as it is an articulated working vehicle.

Industrial applicability

The work vehicle and the method of controlling the work vehicle according to the present invention have the effect of improving the operability during low-speed travel and the stability of linear travel during high-speed travel, and are useful for a wheel loader and the like.

Description of the reference numerals

1, a wheel loader; 2, a vehicle body frame; 3, a working device; 4 front tires; 5a cab; 5a driver seat; 6 an engine compartment; 7 rear tires; 8 a steering operation device; 11 a front frame; 12a rear frame; 13 connecting the shaft parts; 14 big arm; 15, a bucket; 16 a lift cylinder; 17 a bucket cylinder; 18 crank throw; 21a steering cylinder; 21a extending opening; 21b a constriction; 22a steering cylinder; 22a an elongated opening; 22b a constriction; 23 steering hydraulic circuit; a 24-bar joystick; 25 a connecting part; 26 a linkage mechanism; 27 a force applying part; 28 a control unit; 30 main hydraulic circuit; 31 a main hydraulic source; 32 a diverter valve; 33 a valve body; 34 a first pilot chamber; 35 a second pilot chamber; 36 main hydraulic lines; 37 main oil drain pipeline; 38 a first steering line; 39 a second steering line; 40 a pilot hydraulic circuit; 41a variable decompression section; 41a pressure reducing valve; 41b variable relief valves; 42 a pilot valve; 43 a pilot hydraulic source; 44 a pilot hydraulic line; 45 leading oil discharge pipeline; 46 a first pilot conduit; 47 a second pilot conduit; 60 a valve body portion; 61 operating the input shaft; 62 feedback input shaft; 63 a housing; 64a first spring; 64a plate spring portion; 65a second spring; 65a plate spring portion; 66 a feedback part; 71 operating the valve core; 71a cut; 71ae wall portion; 71b cutting; 71be wall portion; 71c holes; 71d holes; 72 operating the sleeve; 72c a groove; 72d groove; 73a feedback spool; 73a cut; 73ae wall portion; 73b, cutting; 73be wall portion; 73c holes; 73d holes; 74 a feedback sleeve; 74c grooves; 74d groove; 75 a drive shaft; 76 a first center pin; 77 a second center pin; (ii) a 80 a steering box; 81a steering operation shaft; 81a rod-side shaft portion; 81b an input shaft portion; 81b1 first end; 81b2 second end; 81c valve side shaft portions; 82 a connecting rod; 83a universal joint portion; 83a central portion; 83b an engagement portion; 83c a joint portion; 84 holes; 91 a follower rod; 92 a follower link; 93 a bracket; 101 a first rotation angle detection unit; 102 a second rotation angle detection unit; 103 a torque sensor; 104 a steering angle detection unit; 105 a vehicle speed sensor; 106 cylinder stroke sensors; 107 cylinder stroke sensors; a 111 motor; 112 worm gear and worm part; 112a cylindrical worm; 112b a worm gear; 204 drive circuit

Claims (6)

1. A working vehicle of an articulated type in which a front frame and a rear frame are coupled to each other, comprising:

a steering lever that changes a steering angle of the front frame with respect to the rear frame by an operation of an operator;

an urging force applying unit that applies an assist urging force or a reaction force to the operation of the joystick by the operator;

a control valve that drives a steering cylinder that causes the front frame and the rear frame to swing and rotate based on the steering angle and an operation of the joystick;

a speed detection unit that detects a speed of the work vehicle;

a steering angle detection unit that detects a steering angle of the rear frame with respect to the front frame;

a first angle detection unit that detects a rotation angle of an operation input shaft of the joystick;

a control unit that controls the acting force applying unit to apply the assist force or the reaction force based on the steering angle detected by the steering angle detecting unit, the rotation angle of the operation input shaft detected by the first angle detecting unit, and the speed detected by the speed detecting unit,

the control unit defines the assist force or the reaction force with respect to a deviation between the steering angle and a rotation angle of the operation input shaft, and controls the force applying unit such that an operation force required for operating the joystick increases as the speed detected by the speed detecting unit increases,

the control unit controls the reaction force applying unit to apply the reaction force when the speed detected by the speed detecting unit is equal to or higher than a predetermined speed set in advance,

and the assist force is applied when the speed detected by the speed detection unit is less than the predetermined speed.

2. The work vehicle of claim 1,

a torque detection unit for detecting a torque generated by the operation of the joystick,

the control unit controls the acting force applying unit to apply an assisting force or a reaction force to the operation of the joystick, based on the torque detected by the torque detecting unit.

3. The work vehicle according to claim 1, characterized by comprising:

a hydraulic actuator that changes the steering angle;

a control valve connected to the joystick and controlling a flow rate of oil supplied to the hydraulic actuator;

the control valve has:

a first input member coupled to the joystick and displaced according to an operation amount of the joystick;

a second input member that is displaced according to the steering angle;

a biasing portion that biases the first input member so as to be located at a neutral position where a displacement amount of the first input member coincides with a displacement amount of the second input member;

the control unit controls a flow rate of oil supplied to the hydraulic actuator based on a difference between a displacement amount of the first input member and a displacement amount of the second input member,

the operating lever is operated against the urging force of the urging portion.

4. The work vehicle of claim 3,

a steering valve that adjusts a flow rate of oil supplied to the hydraulic actuator based on pilot pressure input from the control valve,

the control valve controls a flow rate of oil supplied from the steering valve to the hydraulic actuator by adjusting the pilot pressure.

5. The work vehicle according to claim 1, further comprising:

a hydraulic actuator that changes the steering angle;

a control valve connected to the joystick and controlling a flow rate of oil supplied to the hydraulic actuator;

a connecting portion that connects the lever and the control valve;

the force applying section includes:

a motor that generates the assist force or the reaction force;

and a transmission mechanism that transmits the assist force or the reaction force of the motor to the connection portion.

6. A method for controlling an articulated work vehicle in which a front frame and a rear frame are coupled to each other, comprising:

a speed detection step of detecting a speed of the work vehicle;

a steering angle detection step of detecting a steering angle of the rear frame with respect to the front frame;

a first angle detection step of detecting a rotation angle of an operation input shaft of a joystick that changes a steering angle of the front frame with respect to the rear frame;

a control step of driving a steering cylinder that swings and rotates the front frame and the rear frame based on the steering angle and an operation of the joystick;

an applying step of applying an assist force or a reaction force to the operation of the joystick by the operator based on the steering angle detected by the steering angle detecting step, the rotation angle of the operation input shaft detected by the first angle detecting step, and the speed detected by the speed detecting step,

the applying step defines the assist force or the reaction force with respect to a deviation of the steering angle from a rotation angle of the operation input shaft, and applies the assist force or the reaction force such that the faster the speed detected by the speed detecting step is, the larger the operation force required for the operation of the joystick is,

the applying step applies the reaction force when the speed detected by the speed detecting step is equal to or higher than a predetermined speed set in advance,

and applying the assist force when the speed detected by the speed detecting step is less than the predetermined speed.

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